What is the initial diagnostic approach for a child suspected of having asthma?

Initial Diagnostic Approach for Children Suspected of Having Asthma

The initial diagnostic approach for a child suspected of having asthma should include spirometry, bronchodilator reversibility testing, and fractional exhaled nitric oxide (FeNO) measurement as first-line objective tests, with diagnosis confirmed only when at least two objective test results are abnormal. 1, 2

First-Line Diagnostic Tests

1. Spirometry

• Strongly recommended as part of the initial diagnostic work-up for children aged 5-16 years 1
• Abnormal results supporting asthma diagnosis include:
  • FEV₁/FVC below lower limit of normal (LLN) or <80%
  • FEV₁ < LLN or <80% predicted 1
• Important caveat: Normal spirometry does not exclude asthma, as lung function can be frequently normal during periods of disease stability 1

2. Bronchodilator Reversibility (BDR) Testing

• Should be performed when spirometry shows airflow obstruction
• Positive BDR is defined as ≥12% and/or ≥200 mL improvement in FEV₁ after bronchodilator administration 1
• This test directly assesses variable airflow obstruction, a key feature of asthma

3. Fractional Exhaled Nitric Oxide (FeNO) Measurement

• Should be performed when spirometry is normal
• FeNO ≥25 ppb is considered elevated and supportive of an asthma diagnosis 1
• Reflects eosinophilic airway inflammation characteristic of allergic asthma

Diagnostic Algorithm

1. Perform spirometry first

   • If abnormal → Perform bronchodilator reversibility testing
   • If normal → Perform FeNO measurement

2. Interpret results:

   • Positive diagnosis requires at least two abnormal test results
   • If only one test is abnormal → Consider additional testing or monitoring

3. When tests are inconclusive:

   • For children with abnormal spirometry but negative BDR:
     • A trial of inhaled corticosteroids (ICS) can be considered
     • Repeat objective tests after 4-8 weeks of treatment
     • Important: Diagnosis should not be based on symptom improvement alone, but must include objective improvement in lung function 1, 2

Common Pitfalls to Avoid

1. Diagnosing asthma based on symptoms alone

   • Respiratory symptoms in children are common and often nonspecific 1
   • Wheezing, cough, and breathing difficulties can represent viral respiratory infections or other conditions 1

2. Relying on a single abnormal test

   • The European Respiratory Society explicitly recommends against diagnosing asthma following a single abnormal objective test 1, 2

3. Diagnosing based only on symptom improvement after medication

   • The task force recommends against using improvement in symptoms after a trial of preventer medication alone to diagnose asthma 1, 2
   • Any trial of medication should include objective testing before and after

4. Inadequate spirometry technique

   • Children must be able to perform proper forced expiratory maneuvers
   • Younger children (especially those closer to 5 years) may have difficulty performing adequate spirometry 3
   • Proper coaching and equipment calibration are essential

Special Considerations

• Age appropriateness: The diagnostic approach is valid for children aged 5-16 years, though younger children may have more difficulty with spirometry techniques 1, 3

• Monitoring after diagnosis: Regular monitoring of lung function is essential to detect potential progressive worsening in children with asthma 2

• Alternative tests: For children who cannot perform forced expiratory maneuvers, impulse oscillometry (IOS) may be considered as an alternative tool, as it can be performed during spontaneous breathing 4

By following this evidence-based diagnostic approach, clinicians can reduce both over-diagnosis (which leads to unnecessary medication) and under-diagnosis (which results in untreated symptoms and potential complications) of asthma in children.